Re: [PATCH v4 4/5] mm: make processing of movable_node arch-specific

[Reza Arbab <arbab@linux.vnet.ibm.com>]

On Wed, Oct 26, 2016 at 09:34:18AM +1100, Balbir Singh wrote:
>I still believe we need your changes, I was wondering if we've tested
>it against normal memory nodes and checked if any memblock
>allocations end up there. Michael showed me some memblock
>allocations on node 1 of a two node machine with movable_node

The movable_node option is x86-only. Both of those nodes contain normal 
memory, so allocations on both are allowed.

>> Longer; if you use "movable_node", x86 can identify these nodes at 
>> boot. They call memblock_mark_hotplug() while parsing the SRAT. Then, 
>> when the zones are initialized, those markings are used to determine 
>> ZONE_MOVABLE.
>>
>> We have no analog of this SRAT information, so our movable nodes can 
>> only be created post boot, by hotplugging and explicitly onlining 
>> with online_movable.
>
>Is this true for all of system memory as well or only for nodes
>hotplugged later?

As far as I know, power has nothing like the SRAT that tells us, at 
boot, which memory is hotpluggable. So there is nothing to wire the 
movable_node option up to.

Of course, any memory you hotplug afterwards is, by definition, 
hotpluggable. So we can still create movable nodes that way.

-- 
Reza Arbab